Abstract: This study investigates the genetic variability and environmental adaptability of Acacia hybrid clones across three distinct ecological regions, providing insights into growth characteristics and stem quality for future breed ing strategies. 42 natural hybrid clones were evaluated over a five-year period in three clonal trials in northern, central and southern Vietnam for height (HT), diameter at breast height (DBH), volume (VOL), trunk straightness (STR), branch size (BRA) and survival. Significant clonal differ ences were found in all traits across all three regions. From age 2–5, the clone repeatability ( H²_C ) for growth traits improved from 0.19 to 0.59, indicating substantial genetic control. Genotypic coefficients of variation (CV_G) for vol ume ranged from 21 to 34%, suggesting significant potential for genetic improvement. Site-to-site genotypic correlations ranged from 0.53 to 0.78, pointing to the existence of geno type-environment interactions. Clones derived from Acacia mangium material demonstrated enhanced growth, while the hybrid clones exhibited superior stem quality, particularly in terms of straightness. The findings emphasize the impor tance of selecting clones that are adapted to specific envi ronmental conditions, with both growth and quality traits considered in breeding programs.

Key words: Acacia hybrid, Clonal repeatability, Inter-trait correlation, Age-age correlation, Genotype environment interaction